Process of vulcanizing rubber and product obtained thereby



Patented Dec. 3, 1940 PATENT OFFICE I 1 PROCESS OF VULCANIZING RUBBER AND PRODUCT OBTAINED 'THEREBY Marion W.Harman, Nit-r0, W. Va.,' assignor to Monsanto Chemical Company, St. Louis, M0.,-a corporation of Delaware No Drawing. Application March 25, 1938,

Serial No. 198,112 I 22 Claims.

The present invention relates to a new class of rubber vulcanization accelerators and, to the vulcanization of rubberby. an improved process wherein there isemployed a preferred class of? compounds in the vulcanization process.

The new class of compounds have been found to. accelerate the vulcanization of rubber and in consequence may be employed alone as an accelerator. .In the preferred operation of the present invention, however, the new accelerators are employed in conjunction with other organic accelerators whereby rubber products exhibiting improved properties ,are obtained.

The newand preferred class of accelerators are the cyclohexylamine salts of fatty acids and preferably the cyclohexylamine salts of the high- .er fatty acids as for example cyclohexylamine oleate, cyclohexylamine stearate, dicyclohexylamine stearate, dimethyl cyclohexylamine oleate, dimethyl methyl cyclohexylamine oleate, ,cyclo-, hexylamine laurate, cyclohexylamine. {plienyl stearate, methyl cyclohexylamine oleate, benzyl cyclohexylamine oleate, ethyl cyclohexylamine stearate, cyclohexylamine palmitate and cyclo Thus any substituted hexylamine myristate. ammonia wherein at least one of'the hydrogen atoms is replaced by a cyclohexyl or a .SllbSfi'.

tuted cyclohexyl group, reacted with a higher fatty acid to form a salt is within the, scope of the present invention. 'In place of the fatty acidsdisclosed above, I may-empl'o'yacetic acid, butyric acid, caproic acid, capyrlic acid, capric acid, margaric acid and arachidic acid.

The cyclohexylamine salts of fatty acids are 1 readily obtainable by mixing the proper molecular proportions of th amine with the fatty acid. Where convenient or desirable, the reaction may be enhanced by the-application of heat.

As a specific example of a typical preparation which isiintended to:i1lustrate the invention but not to limitthe same, 28.4 parts by weight (0.1 molecular proportion) of stearic acid and 9.9 parts by weight (0.1Qmolecular proportion) of cyclohexylamine were melted together. A clear liquid was formed which solidified to a soapy white solid upon cooling and this product comprising the desired cyclohexylamine salt of stearic acid was incorporated in typical rubber stocks as hereinafter shown. In like manner cyclohexylamine oleate was-prepared by ,mixing 1 equimolecular proportions of oleic acid and cyclohexylamine. The reaction was exothermic and proceeded without the application of external heat. Other examples of the preferred class of materials are obtainable as described above and the compoundshereinafter employed as specific illustrations of the invention were so obtained. Where convenient or desirable other methodsof'preparation may be employed. Thus an organic solvent may be utilized as a reaction medium or other innovations introduced.

As a specific embodiment of the invention showing the use of the new class of-materials as accelerators for" the vulcanization of rubber but which isintended to illustrate and not to limit the invention, a 'rubberstock was compounded comprising Stock A Partsby weight Smoked sheets 100 Zinc oxide 10 Sulfur, 3 Stearic acid 0.5 Cyclohexylamine oleate 3.0

The rubber stock so compounded was vulcanized at the temperature of twenty pounds steam pressure per square inch and the following modulus and tensile properties were obtained on The above data show the accelerating properties of the preferred class of compounds; 'It is preferred, however, to' employ them in conjunction with other organic accelerators whereby new andimproved results in the vulcanization of rubber are obtained. .Among the said new d. improved. results may be mentioned the valuable softening action possessed by the preferred compounds and by their use the rubber is rendered more plastic and it mills easier so that less power is consumed in the said milling operation. In addition the new compounds show a desirable activation of other organic accelerators when employed in conjunction therewith producing vulcanized rubber products of improved physical properties. In the preferred operation of the present invention the new class of compounds may be employed with any of the usual accelerators commonly employed in the vulcanization of rubber. For example the mercapto thiazole accelerators such as mercaptobenzothiazole, mercapto phenyl benzothiazole, mercapto naphtha thiazole, mercapto methyl thiazole, and mercapto methyl benzothiazole may be employed with the new accelerators of the present invention. It is meant to include by the term mercapto thiazole accelerators reaction products of mercapto thiazoles as well as the free mercapto thiazole. Further examples are the organic base reaction products of mercapto thiazoles exemplified by di(benzothiazyl thiol) dimethyl urea and cyclohexylamino thiol benzothiazole. Other reaction products of mercapto thiazoles have likewise been found applicable in the operation of the present invention as for example dinitro phenyl benzothiazyl sulfide, benzothiazyl thiol benzoate, and methylol thiol benzothiazole and likewise the thiazole sulfides such as dibenzothiazyl mono sulfide and dibenzothiazyl disulfide. In addition other types of accelerators than the mercapto thiazoles may be employed such as the dithiocarbamates and the aldehydeamine accelerators, specific examples of which are sodium dimethyl dithiocarbamate, dimethyl thiuram disulfide, piperidine cyclopentamethylene dithiocarbamate, butylaldehyde-aniline, acetaldehyde-aniline and formaldehyde-aniline.

The following are examples of the preferred operation of the present invention showing the use of the new compounds in conjunction with other accelerators and are to be understood as specific embodiments of the invention and in nowise limitative.

As one specific embodiment of the present invention typical examples of cyclohexylamine salts of fatty acids were employed in conjunction with a mercapto thiazole accelerator. Rubber stocks were compounded comprising Stocks, parts by weight B C D E F G H Smoked sheets 100 100 100 100 100 100 100 Z1110 oxide 5 5 5 5 5 5 5 111 11; s 3 3 3 3 3 a Steanc acid 0.5 0.5 0.5 0.5 0.5 0.5 Mercaptobenzo azole 0.75 0.75 0. 75 0 0 75 0. 1.0 Oyclohexylamine steal-ate 0. 25 Oyolohoxylamine laurate c 0. 25 Oyclohexylamine palmitate 0. 25 Gyclohexylamine phenyl stearate 0.25 Methyl cyclohexylamine oleate 0. 25

and the modulus and tensile properties obtained on testing the cured rubber stocks are given in Table II.

Table II Modulus of elastitcity lbstjin. T 1 t UH: a e onga IODS ensl e a Stock of break in e1ong., lbs/i113 percent B 300 1090 2020 810 C 750 3100 3880 750 D 980 3485 4100 720 E 860 3095 4000 740 F 790 3075 3900 740 G 950 3460 4200 740 H 370 1325 2650 820 B 380 1350 2440 800 C 840 3335 4030 735 D 1080 3760 4650 735 E 905 3270 4125 735 F 870 3100 3850 740 G' 1070 3915 3915 700 H 430 1650 2925 795 B 420 1650 2680 780 O 910 3450 3920 720 D 1030 3830 3830 700 E 945 3330 4180 740 F 900 3290 3900 725 G 1100 3950 3950 700 H 520 1790 2500 770 The above data show that the addition of a small amount of one of the preferred class of materials to a thiazole accelerator, for example mercaptobenzothiazole, gives a faster curing and a higher modulus and tensile stock. This is readily apparent upon comparing the B stock with the C, D, E, F and Gstocks. A comparison of the H stock with the C, D, E, F and G stocks shows that when a portion of the thiazole accelerator is replaced by one of the preferred class of materials, the total accelerator being kept constant, the modulus and tensile properties of the stocks containing the preferred class of materials are again markedly higher than those of the stock Stock 1 Parts by weight Pale crepe V 100 Sulfur 3 Zinc oxide 5 Stearic ac 1 Di(benzothiazyl thiol) dimethyl .urea 0.60 Dimethyl cyclohexylamine oleate 0.10

The rubber stock so compounded was vulcanized in a press at the temperature of twenty pounds steam pressure per square inch and the physical properties of the cured rubber product are given in Table III;

Table III of elastic- 1 m s. inlet Tensile Cure time in elon ations of minutes Stock g at g elong., lbs/in. Percent 500% 700% I 200 V I 670 2000 880 I 320 1240 2680 805 I 385 1610 2800 795 I 525 2160 3250 770 The above data show the desirable modulus and .tensileproperties obtained by the use of --a tertiary cyclohexylamine fatty acid in conjunction with an organic base reaction product of a mercaptothiazole. w

e further specific embodiments of the present invention showing further the use" of the new and preferred class of compounds with organic base reaction products of mercapt'o thiazoles, rubber stocks were compound comprising {The rubber stocks so compounded were vulcanized by heating for different periods of time at the temperatureof twenty pounds steam pressure per square inch andthe'modulus and tensile properties obtained ontesting the cured-rubber products are shown in Table IV. 1 1

I 710070 I V Modulus 01 lasticity in lbs/in. at Tensile Ult Cur;1 itrllllllltee s1n Stock 810I1a010115 ofat livlrleak dong" l -0n. .9 09

J 165 I 437 1203 910 K 170 440 1570 065 J 237 783 1813 875 K 250 775 1680 850 J 325 1125 2300 845 K 287 1048 2210 845 J 393 1300 2700 835 K 344 1250 2610 850 J 405 1455 2745 820 K 393 1430 2815 .830

The above data show the use of the preferred class of materials with organic base reaction products of mercapto thiazoles and the desirable modulus and tensile properties obtained thereby.

'As' a further specific embodiment of the present invention a rubber stock Was: compounded comprising Stock L Parts by weight Smoked sheets 100 Zincoxide 5. Sulfur; 3 Stearic acid 0.50

Cyclohexylamino thiol benzothiazole Cyclohexylamine oleate product are shown in Table V.

organic base reaction product of a mercapto thiazole, for example cyclohexylamino thiobenzothiazole.

As a further specific embodiment of the invention a rubber stock was compouned comprising 7 Stock M Parts by weight Smoked sheets Zinc oxide Whiting Stearic acid Sulfur Methylol thiol benzothiazole 1 Cyclohexylamine oleate 0.25

The rubber stock so compounded was vulcanized in the usual manner at the temperature of sixty pounds steam pressure per square inch and the following modulus and tensile properties obtained on testing the cured rubber product.

Table VI Modulus rig e/lastici y in s. in. Cure time in St k a? elongations g fiii 1Ult.

0c 0 r a -e 0ng., minutes mills-1 s.! percent 500% 700% M 895 2820 3400 745 M 950 3050 3775 745 M 965 3075 3300 726 The above data show the accelerating properties of the preferred class of materials when employed in conjunctionwith the formaldehyde reaction product of a mercapto thiazole, for eX- Stocks, parts by weigh Smoked sheets... 100 100 Zinc oxide 4 4 Noneinforcing carbon black 38 38 Su1fur s 1. 25 l. 25 Aniline-acetone condensation product. treated with mineral acid; .2 1.0 1.0 Benzothiazyl disulfide.-. 0. 7 0. 7 Oyclohexylamine oleate. l. 0 Dicyclohexylamine oleate l 0 The rubber stocks so compounded were vulcanized by heating for different periods of time at thetemperature of sixty pounds steam pressure persquare inch. The modulus and tensile properties of the cured rubber products are given in Table VII.

Table V Table VII Modulus lobf Falas lfiqditilns (1);) 171215;

ticity in sin! Tensile 101 y 1n s. 1n. Tensile Cure time in Stock 82; falongatlons at break gg; Cure time in Stock elongatlons at break gg '7 minutes L unfill aa/ percent nnnutes Tbsp/ m? percent L 755 3300 3950 735 'N 1070 '3005 4180 805 .L 1070 4310 4000 715 0 1 70s 2120 2505 750 L 1340 4700 4700 700 N 1230 3370 4530 800 0 03s 2030 3550 785 N 1190 3205 4305 785 The above data show the desirable modulus and 1010 2810 3780 s00 tensile properties obtained by the use of the pre- 0 ferred class of materials in conjunction with an The above data further show the use of the preferred class of compounds with mercapto thiazole accelerators and the desirable results obtained thereby.

As a further specific embodiment of the invention which is not intended to limit the invention but to illustrate the use of the preferred class of materials with yet another type of organic accelerator, rubber stocks were compoundedcomprising Stocks, parts by weight Smoked sheets 100 Zinc oxide 5 5 Sulfur 3 3 Stearic acid 0. 5 0. 5 Butylaldehyde-aniline condens produc 0. 375 0.375 Cyclohexylamine oleate 0. 25

The rubber stocks so compounded were vulcanized in a press at the temperature of twenty pounds steam pressure per square inch and the following modulus and tensile properties obtained on testing the cured rubber products.

Table VIII a -r a e- 1c1 y in s. 1n. Tensile Cure time in St ck elongatwns at break 5 minutes 0 in lbs/in. Percen P 245 1070 2400 860 Q 295 1390 2660 820 P 375 1690 2975 810 Q 450 2120 3000 760 P 510 2350 3500 790 Q 625 2800 3500 760 P 700 3000 3625 740 Q 775 3480 4025 733 The above data show the marked activation exhibited by the preferred class of materials when employed with aldehyde-amine accelerators.

The new and preferred class of materials may be employed with other, accelerators than those specifically mentioned. This invention is not restricted to the use of the particular compounds given in the disclosure as examples, nor is it restricted to the use of the preferred class of compounds in the particular rubber mixes herein described. The invention is limited only by the claims attached hereto as part of the present specification.

What is claimed is:

1. The process of vulcanizing rubber which comprises heating rubber and sulfur in the pres- 4. The process of vulcanizing rubber which comprises heating rubber, sulfur and a primary cyclohexylamine salt of a fatty acid wherein the fatty acid contains more than eleven but less than twenty-five carbon atoms in the presence of an organic accelerator of a different class.

5. The process of vulcanizing rubber which comprises heating rubber, sulfur and a mercapto thiazole accelerator in the presence of a primary cyclohexylamine salt of a fatty acid.

6. The process of vulcanizing rubber which comprises heating rubber and sulfur in the presence of cyclohexylamine oleate.

7. The process of vulcanizing rubber which comprises heating rubber, sulfur and a mercapto thiazole accelerator in the presence of cyclohexylamine oleate.

8. The process of Vulcanizing rubber which comprises heating rubber and sulfur in the presence of a primary cyclohexylamine oleate.

9. The process of vulcanizing rubber which comprises heating rubber, sulfur and a mercapto thiazole accelerator in the presence of a primary cyclohexylamine oleate.

10. The process of vulcanizing rubber which comprises heating rubber and sulfur in the presence of cyclohexylamine stearate.

11. The process of vulcanizing rubber which comprises heating rubber, sulfur and a mercapto thiazole accelerator in the presence of cyclohexylamine stearate.

12. The rubber composition comprising rubber, sulfur and a primary cyclohexylamine salt of a. fatty acid.

13. The rubber composition comprising rubber, sulfur and a primary cyclohexylamine salt of a fatty acid wherein the fatty acid radical contains more than eleven but less than twenty-five carbon atoms.

14. The rubber composition comprising rubber, sulfur a primary cyclohexylamine salt of a fatty acid and an organic accelerator of a different class.

15. The rubber composition comprising rubber, sulfur a primary cyclohexylamine salt of a. fatty acid wherein the fatty acid contains more than eleven but less than twenty-five carbon atoms and an organic accelerator of a different class.

16. The rubber composition comprising rubber, sulfur a mercapto thiazole accelerator and a primary cyclohexylamine salt of a fatty acid.

1'7. The rubber composition comprising'rubber, sulfur and cyclohexylamine oleate.

18. The rubber composition comprising rubber, sulfur a mercapto thiazole accelerator and cyclohexylamine oleate.

19. The rubber composition comprising rubber, sulfur and a primary cyclohexylamine oleate.

20. The rubber composition comprising rubber, sulfur a mercapto thiazole accelerator and a primary cyclohexylamine oleate.

21. The rubberv composition comprising rubber, sulfur and cyclohexylamine stearate.

22. The rubber composition comprising rubber, sulfur'a mercapto thiazole accelerator and cyclohexylamine stearate. 

